At the end of Parshas Bo, the Torah mentions tefillin twice. The first time the Torah commands us:

והיה לך לאות על-ידך ולזכרון בין עיניך

Rabbi Aryeh Kaplan zt”l translates this verse, “[These words] must also be a sign on your arm and a reminder in the center of your head” (Shemos 13:9).

A few verses later, the Torah again mentions tefillin, but this time describes the Shel Rosh a bit differently:

והיה לאות על ידכה ולטוטפת בין עיניך

Rabbi Kaplan translates this verse, “[These words] shall [also] be a sign on your arm and an insignia in the center of your head.” The Targum Onkeles renders the word totafos as tefillin, which connotes prayer, judgment and testimony. In Greek they were known as phylacteries, from the root phylassin, which means to watch or guard.